Neutrons are widely utilized in order to detect nuclear materials, explore oil layers, research the structure of materials and study medicine. Accordingly, a generating source for the neutron has been researched and developed as necessary.
A neutron may be obtained basically by causing a nuclear fusion reaction expressed as follows:D++D+→n+He3 or D++T+→n+He
There have been, inter alia, trials to generate neutrons in a high flux by nuclear fusion reaction utilizing plasma. Japan Patent Laid-Open Publication No. 2008-202942 also discloses a nuclear fusion reaction using plasma, but adopts a configuration that separately installs a space for plasma generation outside a space for the nuclear fusion reaction and sets an ion extraction electrode in a space which the nuclear fusion takes place in, which makes an equipment complicated and lowers the efficiency of nuclear fusion.
Meanwhile, there is a method to produce a neutron flux by causing a target on which substances such as deuterium are adsorbed to be collided utilizing plasma generated from an RF (radio frequency) ICP (inductively coupled plasma) plasma source. In this method, to produce a high neutron flux, ions accelerated and extracted by plasma sheath generated between plasma and target are caused to collide with the target, instead causing the ion to collide with the target by extracting the ions from the conventional ion sources.
The above-described method, however, poses a few problems as follows.
When the target is immersed in RF ICP plasma, the temperature in the target surface is drastically heated by collision with the ions and electrons in the plasma, which leads a considerable evaporation of reactant elements adsorbed on the metallic surface of the target. For instance, in a case in which heavy hydrogen is absorbed on a Ti target, it commences evaporation at 200° C., which brings down the probability of nuclear fusion, thereby lowering the neutron flux. To deal with such a problem, installing an additional cooling unit for the target may be considered but it may not extend significantly the target life.
Another problem is that the magnetic field generated in the vicinity of the target may cause the reverse effect to the original intension. A magnetic field generated in the vicinity of the target, for example, prohibits the ions in the RF ICP plasma from diffusing to the vicinity of the target, which rather lowers the density of the plasma in the vicinity of the target and lowers the ion flux that collides with the target thereby lowering the neutron flux. In other words, the generated plasma itself may not approach the target that is inside the magnetic field due to the effect of the magnetic field. Accordingly, the neutron generating source having such a structure may not produce a high neutron flux.
In addition, the conventional neutron or gamma ray generating sources, which utilize the nuclear fusion reaction by causing the ions to collide with the target, use the target on which the reactant elements are adsorbed from outside. However, when such a target is used for a neutron or gamma ray generating source, since the target has a relatively short life, it is necessary to continuously supply the targets from the outside. Accordingly, the conventional neutron or gamma ray generating source is hardly operated continuously for long time.